1. Field of the Invention
The present invention relates to a configuration method for a data management system, for accessing data in a distributed data structure.
The distributed data structure involved may be provided by many different arrangements. For instance, it might be provided by different nodes in a parallel processing computer. In a communications network on the other hand, it might be provided at different switching points in the network, for instance at local exchanges of a public network. In a particular example, the invention can be used to provide routing information to route calls to users who can change their position with respect to logical or geographic locations in the network.
2. Related Art
Services available by means of communication networks are becoming increasingly complex. It has become important to introduce management systems for the associated service features, which may be selectively available to a customer, whilst not introducing excessive computing or communications overheads. An example is known as personalised telephone numbering schemes. In these, each user, or group of users, might be allocated a telephone number which remains unchanged when the user or users change their location in the network.
For a service such as personal numbering, it is clearly important that location data can be readily changed. From the point of view of the network, the location data is volatile but must always be quickly accessible in its current version.
Another aspect of a network service such as personal numbering is that it is likely to be important that it is scalable. That is, it needs to be capable of being expanded to a much larger, perhaps indefinite, number of users. For instance, it is likely to be important that a network system can grow to support a matter of millions of users. It is also likely that these users will generate variable load. For instance, users arriving at the office may wish to transfer their personal number from their home location to their office location. This would generate several million transactions in the space of a few hours. If a fixed network were to support a fully mobile service, equivalent to that of a cellular radio network, then the overhead carried by the fixed network in updating location information could lead to many millions of transactions every hour.
It is an option to maintain a central database, holding the data relevant to a service such as personal numbering. Any traffic which needs to be routed to a destination in the network may then access the database to obtain a current location for the destination. However, a system of this type generates a significant overhead in that the network must carry traffic simply accessing the central database, either to update location data or to download a current version. An arrangement based on central control is clearly vulnerable to overload.
Another approach, used in cellular (mobile) telephone networks, is to provide each user with a home register, known as a "Home Location Register". Each home register holds data relevant to the user, of the type sometimes known in intelligent network technology as a user profile. That is, it might for instance indicate which services that user subscribes to and give details such as time of day information in relation to services of the "call divert" type which can apply differently at different times of day. It will also contain location data for the user. The home registers together effectively provide a distributed data structure and are allocated so that there is mapping between users' usual locations and the position of their home registers in the network. However, because all calls automatically go to the called user's home register, there is still a significant overhead in dealing with the user when away from his/her usual location. Additionally, changes in the user's location mean the location data in the home register has to be updated, which adds to the signalling load. Further, there are problems as the size of the customer base grows. The design response in a cellular network to an increasing customer base is to decrease the local cell sizes. However, not only does the signalling load grow dramatically, according to a square law, but so does the complexity of the management procedures. Providing data integrity and robustness become significant issues.
A slightly more sophisticated version of the "Home Location Register" (HLR) arrangement has been proposed, in which an additional register is provided, this being known as the "Visited Location Register". It repeats the character of the HLR but is located elsewhere in the network, to deal with call requests when the called user is away from his/her usual location. Incoming calls will be referred to either Register in these circumstances, depending on where the incoming call arises in the network. If a call request is routed to the HLR however, it is simply passed on to the Visited Location Register.